The following tests may be used to diagnose colon cancer or find out if it has spread. Tests also may be used to find out if surrounding tissues or organs have been damaged by treatment.

Digital rectal exam (DRE): The doctor inserts a gloved finger into the rectum to feel for polyps or other problems.

Fecal occult blood test (FOBT): This take-home test finds blood in stool.

Fecal immunochemical test (FIT): This take-home test finds blood proteins in stool.

Endoscopic tests, which may include:
Sigmoidoscopy: A tiny camera on flexible plastic tubing (sigmoidoscope) is inserted into the rectum. This gives the doctor a view of the rectum and lower colon. Tissue or polyps can be removed and looked at under a microscope.
Colonoscopy: A longer version of a sigmoidoscope, a colonscope can look at the entire colon.
Endoscopic ultrasound (EUS): An endoscope is inserted into the rectum. A probe at the end bounces high-energy sound waves (ultrasound) off internal organs to make a picture (sonogram). Also called endosonography.

Imaging tests, which may include:
CT or CAT (computed axial tomography) scan
MRI (magnetic resonance imaging) scan
PET/CT (positron emission tomography) scan
Virtual colonoscopy or CT (computed tomography) colonoscopy
Double contrast barium enema (DCBE): Barium is a chemical that allows the bowel lining to show up on an X-ray. A barium solution is given by enema, and then a series of X-rays are taken.
Blood test for carcinoembryonic antigen (CEA): CEA is a protein, or tumor marker, made by some cancerous tumors. This test also can be used to find out if the tumor is growing or has come back after treatment.